In 3GPP RAN Session #65, Licensed-assisted access (LAA) has been approved to enable LTE usage over unlicensed spectrum for small cells. To have an efficient and fair spectrum sharing, a dynamic spectrum sharing mechanism called listen-before-talk (LBT) needs to be supported in European and Japan. In 3GPP meeting, the modified load based equipment (LBE) is used for the transmission burst. Due to the LBE mechanism, there may be fractional subframes in the beginning or end. To support the transmission of fractional subframe, an initial signal is designed for channel reservation, detection of the transmission burst, and coarse time/frequency synchronization. A discovery reference signal (DRS) is required for the unlicensed band operation. For UE measurement, a DRS measurement timing configuration (DMTC) is configured with a periodicity. Under the LBE, when a data transmission collides with the DMTC, wherein the DRS is to be transmitted, how to multiplex DRS in the transmit opportunity (TxOP) remains an issue. Further, how to allocate the PDSCH in the subframe that contains the DRS remains a question as well.
Improvements and enhancements are required for multiplexing DRS within a transmission burst for opportunistic spectrum access.